Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, which are suitable for an image pickup apparatus using a solid-state image pickup element, such as a video camera, an electronic still camera, a broadcasting camera, and a monitoring camera, or an image pickup apparatus such as a silver-halide film camera.
Description of the Related Art
A zoom lens which has a short total lens length, a compact size, a high zoom ratio, and a high resolving power has been requested for an imaging optical system used in an image pickup apparatus. It is known that a positive-lead type zoom lens in which a lens unit having a positive refractive power is arranged closest to an object side easily achieves a high zoom ratio.
In Japanese Patent Application Laid-Open Nos. 2007-178598 and 2007-178769, there is disclosed a five-unit zoom lens which includes first to fifth lens units having positive, negative, positive, positive, and negative refractive powers and being arranged in order from an object side to an image side.
In a zoom lens in general, in order to realize the downsizing of the entire system while the high zoom ratio is ensured, it is only necessary to reduce the number of lenses while increasing the refractive powers of the lens units constructing the zoom lens. However, in the zoom lens configured in such a manner, a lens thickness increases with an increase in the refractive power of each of the lens surfaces, and an effect of shortening the lens system becomes insufficient. Further, various aberrations are frequently generated, and hence the satisfactory correction for the various aberrations becomes difficult to carry out. Thus, the high optical performance becomes difficult to obtain.
In the positive-lead type five-unit zoom lens described above, in order to realize the downsizing of the entire system, the high zoom ratio, and the high optical performance over the entire zoom range at the same time, it is important to set each element of the zoom lens appropriately. For example, it is important to set the refractive power of the second lens unit for varying magnification, which moves during zooming, the lens structure of the second lens unit, and the like appropriately. When those configurations are not appropriate, the entire system is increased in size in realizing the high zoom ratio, variations in various aberrations accompanying zooming are increased, and it becomes very difficult to obtain the high optical performance over the entire zoom range.